ectomycorrhiza (pl. ectomycorrhizae) a symbiotic association between a nonpathogenic or weakly pathogenic fungus and the roots of plants with fungal hyphae between and external to root cells (contrasts with arbuscular mycorrhiza, endomycorrhiza)

ectoparasitea parasite that feeds from the exterior of its host (contrasts with endoparasite)

electron microscopea microscope that uses a focused beam of electrons to produce a greatly enlarged image of minute objects, such as a virus, in the same way that light is used in a compound microscope

elicitora molecule produced by the host (or pathogen) that induces a response by the pathogen (or host)

ELISA (acronym for enzyme-linked immunosorbent assay) a serological test in which the sensitivity of the reaction is increased by attaching an enzyme that produces a colored product to one of the reactants

embryoan organism in the early stages of development, such as a young plant in the seed, or a nematode before hatching from the egg

emergencethe growth of the seedling shoot through the surface of the soil

endomycorrhiza (pl. endomycorrhizae) a symbiotic association between a nonpathogenic or weakly pathogenic fungus and the roots of plants in which fungal hyphae invade cortical cells of the root (see also arbuscular mycorrhiza) (contrasts with ectomycorrhiza)

endoparasitea parasitic organism that lives and feeds from inside its host (contrasts with ectoparasite)

endophytea plant developing inside another organism; also used for endoparasitic fungi found in grass species

endoplasmic reticulumthe system of interconnected cytoplasmic membranes that transports materials within the cell

endospermthe nutritive tissue formed within the embryo sac of seed plants

endosporea resistant, thick-walled asexual spore formed within a bacterial or fungal cell

Environmental Protection Agency(acronym EPA)the U.S. federal agency responsible for controlling the various aspects of air, water, and soil pollution, including pesticide regulations

enzyme-linked immunosorbent assay (acronym ELISA) a serological test in which the sensitivity of the reaction is increased by attaching an enzyme that produces a colored product to one of the reactants

EPA (acronym for Environmental Protection Agency) the U.S. federal agency responsible for controlling the various aspects of air, water, and soil pollution, including pesticide regulations

epicotylthe portion of the stem of a plant embryo or seedling above the node where the cotyledons are attached (contrasts with hypocotyl)

epidemican increase of disease in a population; a general and serious outbreak of disease (see also epiphytotic)

epidemiology (adj. epidemiologic) the study of factors influencing the initiation, development, and spread of infectious disease; the study of disease in populations

epidermis (adj. epidermal) the surface layer of cells of leaves and other plant parts

EPS (acronym for extracellular polysaccharide) a sugar polymer that aids in movement, helps prevent desiccation, and contributes to the slimy appearance of bacteria, fungi, and nematodes; and probably promotes colonization of plant tissues and disease development in bacteria

eradicationthe management of plant disease by eliminating the pathogen after it is established or by eliminating the plants that carry the pathogen

ergota disease of certain grasses and cereals, especially rye, caused by Claviceps spp.; a sclerotium, or resting structure, produced by Claviceps spp. and other closely related fungi in infected flowers of parasitized grain plants

ergotisma disease of humans and other animals caused by ingestion of grain contaminated with alkaloids of ergot fungi, often called the holy fire or St. Anthony's fire in the Middle Ages

extracellular polysaccharide (acronym EPS) a sugar polymer that aids in movement, helps prevent desiccation, and contributes to the slimy appearance of bacteria, fungi, and nematodes; and probably promotes colonization of plant tissues and disease development in bacteria

extrachromosomal inheritancethe inheritance of genes not located in the nucleus, i.e., those in mitochondria and chloroplasts (see also cytoplasmic inheritance, maternal inheritance)

exudatea liquid excreted or discharged from diseased tissues, from roots and leaves, or by fungi

f. sp. (abbr. for forma specialis) a taxonomic group within a pathogenic fungal species defined in terms of host range, i.e., members of different formae speciales infect different groups of plants; forma specialis for fungi is equivalent to pathovar for bacteria

facultativecapable of changing life-style, e.g. from saprophytic to parasitic or the reverse

forest declinethe combination of biotic factors (e.g. insect pests, pathogens) and abiotic factors (e.g. drought, air pollution) that contributes to poor growth and death of populations of trees

form genusa genus based on morphology and not on evolutionary relationships, such as used for imperfect fungi

forma specialis (abbr. f.sp.; pl. formae speciales) a taxonomic group within a pathogenic fungal species defined in terms of host range, i.e., members of different formae speciales infect different groups of plants; forma specialis for fungi is equivalent to pathovar for bacteria

fossil waterthe water in aquifers that has accumulated over long periods of time and is not quickly replaced through infiltration from recent rainfall

fumigant (v. fumigate) a gas or volatile substance used to kill or inhibit the growth of microorganisms or other pests

Fungi Imperfectian archaic term for a group of fungi without a sexual stage; also, the asexual stage of members of Ascomycota (the ascomycetes) and Basidiomycota (the basidiomycetes) (see also deuteromycetes, imperfect fungi)

fungicide (adj. fungicidal) a chemical or physical agent that kills or inhibits the growth of fungi

fungistasisthe inhibition of fungal growth, sporulation, or spore germination but not death; used to describe the nonspecific phenomenon in natural soils where spore germination is inhibited and often overcome by rhizosphere nutrients

fungistat (adj. fungistatic) a chemical or physical agent that inhibits fungal growth, sporulation, or spore geminiation, but does not cause death

fungus (pl. fungi) a eukaryotic organism that is usually filamentous (forming a mycelium) and heterotrophic, has cell walls composed of chitin, and reproduces by sexual and/or asexual spores

gene silencingthe switching off of a gene by a process other than genetic modification; one example is the disabling of a gene by small interfering RNAs (siRNAs) that target messenger RNA for destruction

gene-for-gene hypothesisthe hypothesis that corresponding genes for resistance and virulence exist in the host and pathogen, respectively

general resistancea resistance that is effective against all biotypes of the pathogen (see also durable resistance, horizontal resistance, race-nonspecific resistance) (contrasts with specific resistance, vertical resistance)

graftthe transfer of aerial parts of one plant (e.g. buds or twigs - the scion) into close cambial contact with the root or trunk (the rootstock) of a different plant; a method of plant propagation; the joining of cut surfaces or growing roots of two plants to form a living union

graft transmissionthe transmission of a pathogen from one host plant to another through fusion of living tissue from the diseased host with living tissue of a healthy host

Gram-negativethe bacteria staining red or pink in the Gram staining procedure after treatment with Gram's stain

Gram-positivethe bacteria staining violet or purple in the Gram staining procedure after treatment with Gram's stain

Gram staina procedure used for identification of bacteria in which crystal violet stain, Gram's iodine, ethyl alcohol and safranin stain are applied in succession to cells of the bacteria

green manurea crop plowed under while still green and growing to improve the soil; sometimes used to enhance populations of antagonistic microorganisms for biological control

greenhouse effectthe heating of the atmosphere as radiation from the sun is converted to infrared radiation but is trapped by so-called greenhouse gases (i.e., water vapor, CO2, methane, ozone), preventing its release; this is similar to a greenhouse, in which glass traps air heated by infrared radiation

groundwaterthe water contained in aquifers in the soil, sometimes in underground rivers but more often in small accumulations mixed with sand

growth regulatora chemical substance produced in one part of an organism and transported in minute quantities to induce a growth response in another part, e.g., in plants, auxins, cytokinins, and gibberellins (see also hormone)

haustorium (pl. haustoria) a specialized branch of a parasite formed inside host cells to absorb nutrients

headin plants, a type of inflorescence in which numerous small flowers are densely crowded on a disk or around a central stalk

heartwoodthe central cylinder of nonfunctional xylem in a woody stem (contrasts with sapwood)

hemiparasitea parasitic flowering plant that contains chlorophyll when mature (photosynthetic) and obtains water with dissolved nutrients by connecting to the host xylem via the haustorium, e.g., true mistletoe (Phoradendron spp. or Viscum spp.) or witchweed (Striga spp.) (contrasts with holoparasite)

herbaceousdescribing primary, soft, nonwoody tissue, as a plant or plant part; having the characteristics of an herb

herbicidea chemical used for killing plants or inhibiting plant growth, e.g., a weed or grass killer

heritabilitya measure of the ability of a characteristic to be passed from one generation to the next

hermaphrodite (adj. hermaphroditic) having both male and female reproductive organs

heteroeciouspertaining to a rust fungus requiring two unrelated host plants for completion of its life cycle (contrasts with autoecious)

heterokaryon (adj. heterokaryotic) a cell with genetically different nuclei

heterosisthe increased vigor of hybrid offspring when compared to either parent (see also hybrid vigor)

heterothallism (adj. heterothallic) the condition in which sexual reproduction can occur only in the presence of genetically different mycelia (contrasts with homothallism)

heterotrophan organism that obtains nourishment from outside sources and must obtain its carbon from organic carbon compounds (contrasts with autotroph)

heterozygoushaving alternate forms (allele) of a gene on homologous chromosomes (contrasts with homozygous)

holomorphthe whole fungus in all its states (contrasts with anamorph, imperfect state, perfect state, teleomorph)

holoparasitea parasitic flowering plant that lacks chlorophyll (nonphotosynthetic) and must rely totally on the contents of the xylem and the phloem of the host plant, e.g., broomrape (Orobanche spp.) (contrasts with hemiparasite)

homothallism (adj. homothallic) a condition in which sexual reproduction occurs with a single thallus; self-fertile (contrasts with heterothallism)

homozygoushaving the same form (allele) of a gene on homologous chromosomes (contrasts with heterozygous)

honeydewthe sugary ooze or exudate, often from aphids, and a characteristic symptom of ergot

horizontal resistancea resistance which is effective against all biotypes of the pathogen (see also durable resistance, general resistance, race-nonspecific resistance) (contrasts with specific resistance, vertical resistance)

hormonea chemical substance produced in one part of a an organism and transported in minute quantities to induce a growth response in another part, e.g., in plants, auxin, cytokinin, and gibberellin (see also growth regulator)

host planta living plant attacked by or harboring a parasite or pathogen and from which the invader obtains part or all of its nourishment

host rangethe range of plants on which an organism, particularly a parasite, feeds

HR (acronym for hypersensitive response)the rapid and localized cell death at the site of infection in resistant interactions between plants and pathogens

hyalinetransparent or nearly so; translucent; often used in the sense of colorless

hybrid (v. hybridize) the offspring of two individuals of different genotypes

hybrid vigorthe increased vigor of hybrid offspring when compared to either parent (see also heterosis)

hybridomaa cell produced by the fusion of an antibody-producing cell and a lymphoma (cancer) cell for production of monoclonal antibodies

hyphomycetesan archaic term for the deuteromycetes (Fungi imperfecti, the imperfect fungi) that produce conidia freely or on a sporodochium or synnema (contrasts with coelomycetes)

hyphopodiuma stalked, thick-walled, lobed cells that stick to plant surfaces; sometimes used to describe the infection structures produced by ectotrophic hyphae of certain root-infecting fungi such as Gaeumannomyces (take-all pathogen)

hypocotylthe portion of the stem below the cotyledons and above the root (see epicotyl)